The present invention relates to a differential assembly, and more particularly, to the lubrication of the rolling element support bearings for the pinion shaft of the differential assembly.
Differential assemblies are well known and arranged in the drive train system of a motor vehicle to allow a pair of output shafts, operatively coupled to an input shaft, to rotate at different speeds. As the output shafts are connected to the wheels of the vehicle, this function is required to allow the outer drive wheel to rotate faster than the inner drive wheel while the vehicle is turning. Differential assemblies utilize rolling element bearings to support the pinion shaft which provides rotational input to the output shafts.
Rolling element bearings require lubrication to keep the bearing components cool and maintain a required lubrication film thickness, both of which are required to meet bearing lifetime requirements. Excessive lubrication can be detrimental and impose a drag, termed as churning losses, on the rolling element bearing, resulting in an undesirable increase in friction.
Referring to FIG. 1, a cross-sectional view of a prior art differential assembly is shown. The differential assembly 100 contains a housing 102 along with a ring gear 104, a pinion shaft 106 and a pinion gear 108. The pinion shaft is supported by a pinion head bearing 110 and a pinion tail bearing 112. A sleeve 114 abuts against the respective inner rings of the two bearings, assisting with applying the necessary pre-load for optimum operating clearance purposes. The differential housing contains lubricant to a level L, resulting in portions of the pinion gear 108, the ring gear 104, the pinion head bearing 110 and the pinion tail bearing 112 being immersed in lubricant when the vehicle is on level ground. The pinion shaft 106 provides rotational input to the ring gear 104 via the pinion gear 108. As rotation and subsequent meshing of the gears occurs, oil is splashed within the housing 102. The splash lubricant follows a path through a port 116 indicated by the arrows to reach the space between the bearings, providing both bearings 110, 112 with lubricant. This path of oil is particularly vital to the pinion tail bearing 112 during low lubricant level conditions or when the vehicle is travelling downhill and the lubricant moves away from the tail bearing. Due to the proximity of the pinion head bearing 110 to the pinion gear 108, the pinion head bearing 110 receives splash lubrication from the pinion gear interface with the ring gear 104. Therefore, the pinion head bearing 110 receives lubrication from both sides, exceeding the amount of lubrication provided to the pinion tail bearing 112 during most operating conditions and oil level conditions. In order to ensure adequate lubrication is delivered to the pinion tail bearing, the port 116 must be arranged to capture and direct enough lubricant to ensure that the lifetime requirement of the pinion tail bearing 112 is met during the worst case lubrication conditions. The disadvantage of this strategy is that excessive lubrication is provided to the pinion head bearing 110 which yields higher bearing friction due to churning losses. It is necessary to provide adequate, but not excessive lubrication to both of the bearings for optimum efficiency of the differential assembly.